Measuring wave front distortions is well known in optics, and is essential for adaptive optics. There are a few known wave front sensors that work on similar elements: an optical part that transforms the aberrations into a light intensity variation and determines the response of the wave front sensor, a detector that transforms the light intensity into electrical signals, and a reconstructor that converts the signals into phase aberrations.
The case of adaptive optics will serve here as an example of an application for measurement of wave fronts, but there are other applications which require measuring wave fronts, such as optical shop testing, wafer measurements, and many more. Most astronomical adaptive optics systems use either a Hartmann-Shack wave front sensor or a curvature sensor. There are some cases where the temporal frequency of the turbulence changes with time. These cases are difficult to deal with, since the geometry of the sensors is constant and cannot be easily changed. When the number of photons is limited, it is advantageous to minimize the number of pixels in the detector to improve the signal to noise ratio in each pixel. The best detectors, currently single avalanche photodiodes, are slowly being replaced by continuous cameras such as CCDs (charge-coupled-devices) in order to measure the wave front at different spacings. This is achieved by zooming (changing the magnification) of the relayed aperture onto the wave front sensor or replacing one lenslet array with another, having a different frequency (M. E. Kasper et al., “ALFA: adaptive optics for the Calar Alto Observatory optics, control systems, and performance”, Experimental Astronomy 10, 49–73, 2000).
Similar problems arise in ocular adaptive optics, where turbulence is replaced by variable aberrations in the cornea and inside the eye, and where large variations exist between different subjects. Other applications of adaptive optics may require variable spatial and dynamic range sensitivity, such as for open-air communications, microscopy, laser power transfer, and more. Another very important field, in which photons are more plentiful, is measurement of optical surfaces and components, such as for optical shop testing. The wave fronts exiting these systems can have very large aberrations, which need to be measured on a very fine lateral scale. Light from segmented optics, such as in large telescopes, is an extreme case of ill-behaved wave fronts.
There is a need for simple wave front sensor that can measure wave fronts under severe conditions such as low light level, fast scale variations, large aberrations, wide dynamic range, both lateral and in depth, and discontinuities in the wave front. The variable lenslet array of the present invention fulfils the need to sense wave fronts under severe conditions.